A model of alteration and maturation of the Martian surface
material is described involving both chemical and physical
interactions. Physical processes involve distribution and
mixing of the fine-grained soil particles across the surface
and into the atmosphere. Chemical processes include reaction
of sulfate, salt and oxidizing components of the soil
particles; these agents in the soils deposited on rocks will
chew through the rock minerals forming coatings and will
bind surface soils together to form duricrust deposits.
Formation of crystalline iron oxide/oxyhydroxide minerals
through hydrothermal processes and of poorly crystalline and
amorphous phases through palagonitic processes both
contribute to formation of the soil particles. Chemical and
physical alteration of these soil minerals and phases
contribute to producing the chemical, magnetic and
spectroscopic character of the Martian soil as observed by
Mars Pathfinder and Mars Global Surveyor. Minerals such as
maghemite/magnetite and jarosite/alunite have been observed
in terrestrial volcanic soils near steam vents and may be
important components of the Martian surface material. The
spectroscopic properties of several terrestrial volcanic
soils containing these minerals have been analyzed and
evaluated in terms of the spectroscopic character of the
surface material on Mars.